It is conventionally known to use activated charcoal and other materials as adsorptive elements to remove impurities from an air stream. With the advent of effective fiber cross sections, it is possible to produce fibers which are partially hollow. A particularly effective cross section is one having three T-shaped lobes extending from a central core, as described in U.S. Pat. No. 5,057,368, “Filaments Having Trilobal Or Quadrilobal Cross-Sections” to Largman et al., which is incorporated herein by reference. Conventional filters have used filtering media coated with solid or liquid materials in a variety of applications; however, many of these applications have relied on absorption, rather than adsorption. Adsorption occurs where particles to be removed attach to the surface of the filter material elements; whereas, absorption occurs where molecular motion mobility is harnessed to move unwanted particles from one zone to another in a non-mechanical manner. The multilobal fiber has been particularly effective as a wicking fiber where certain contaminant-removing liquids or solids are filled in cavities formed within the fiber.
The multilobal fiber filled with solid filtering particles have been used in adsorptive air filtration and odor-removing applications. Such filtering particles have included the use of carbon particles, zeolites, baking soda, cyclodextrins, and solids which could adsorb certain contaminants (see U.S. Pat. No. 5,759,394, which is incorporated herein by reference). Other applications utilizing multilobal-type fibers as wicking fibers also have involved absorptive properties of certain liquids which are filled within the cavities of the fibers. These liquids were typically chosen to lightly absorb odor and gas molecules in a reversible manner from a contaminated air stream to aid in the eventual dispersion of these molecules into a second air stream (see U.S. Pat. Nos. 5,891,221 and 5,704,966, which are incorporated herein by reference).
Maintaining environments free of contaminants is particularly critical in the manufacturing of integrated circuits because wafers are very susceptible to small particles and low levels of certain chemicals. This can be done by manufacturing wafers inside clean rooms with filtered air. The filters are used to reduce particle and chemical levels to extremely low levels (less than 1 part-per-billion). Semiconductor tools are also sometimes equipped with environmental controls that provide local ultra clean airflow during processing. However, conventional chemical filters have a very short life span, require frequent replacement, and are ineffective at efficiently filtering out certain chemicals.
The priority application teaches filtering of basic gases using fibers having longitudinally extending internal cavities that contain a reagent that chemically reacts with the basic gas. Preferred reagents include an acid, a coordinating agent, a complexing agent, and a deliquescent agent, and may advantageously be impregnated into an adsorptive solid. At the time, it was not recognized that basic gases could also be filtered using an oxidizing reagent, or that acidic or neutral gases could be filtered in an analogous manner. Thus, there is still a need to provide devices and methods for filtering various gases.